Electron Spin Dynamics in Non-Magnetic Narrow Gap Semiconductors
Ben Murdin
The University of Surrey
Measurement and control of spin dynamics in semiconductors is important for
development of semiconductor spintronic devices. Semiconductors with large atom
constituents that bring large spin-orbit coupling effects typically also have small gap.
We have developed new techniques for investigation of spin dynamics in such
materials, and have investigated spin injection and control from ferromagnetic metals.
We have developed a mid- and far-infrared femtosecond time-resolved Larmor
precession technique for investigation of spin dynamics in such materials, and have
applied it to InSb from 77 to 300 K. The optically oriented polarization precesses
coherently even at 300 K, and we show that the precession rate is in the THz range
even for small field <<1T. The inferred Zeeman spin splitting is strongly energy
dependent, and the electron g factor (g*) is in good agreement with a semi-empirical
(k*p) theory of the electronic structure. However, we also show that the most widely
quoted formula for g* in GaAs (due to Hermann and Weisbuch) is incomplete and
contains an error of as much as 30%. We have used two-colour pump-probe
experiments using the free-electron laser to investigate the relative contributions of
spin-dephasing and spin flip scattering in both bulk materials and quantum wells.
Finally, we have investigated electroluminescence characteristics of hybrid narrow
gap semiconductor light-emitting diodes with ferromagnetic metal injectors at low
temperatures (of ~ 10K) and in magnetic fields up to 2T. For FeCo injectors on
InAsSb quantum wells with AlOx tunnel barriers we find an injection polarisation of
35% (+/-5%) at 1T, which is almost the theoretical maximum for this material (40%).